1. Field of the Invention
The present invention relates to a PTO transmission structure for externally drawing out power from a driving source, which PTO transmission structure is inserted with a PTO clutch unit.
2. Related Art
In working vehicles such as tractors, a PTO system transmission mechanism for externally outputting power from a driving source is provided in addition to a traveling system transmission mechanism for transmitting power from the driving source to driving wheels (see e.g., JP-A 2003-94970, which will be hereinafter referred to as “cited reference”).
As described in the cited reference, the PTO system transmission mechanism normally includes a PTO clutch unit for selectively engaging/interrupting the power transmission from the driving source, and is configured to allow drawing of power only when necessary.
The PTO clutch unit is arranged between a PTO driving shaft operatively connected to the driving source and a PTO driven shaft arranged on a downstream side in the transmission direction of the PTO driving shaft; however, in the conventional PTO system transmission mechanism, the assembling task of the PTO clutch unit cannot be efficiently carried out.
That is, in the conventional PTO system transmission mechanism, a transmission case includes a transmission case main body having a wall integrally formed therein at the rear of a differential gear unit, which transmission case main body being opened at the downstream side (generally, at the rear in the longitudinal direction of a vehicle) in the transmission direction, and a lid member connected to the transmission case main body so as to block the opening.
The PTO clutch unit and the PTO driven shaft are incorporated in the transmission case through the opening, and are supported by the wall of the transmission case main body and the lid member.
In the conventional configuration, the lid member must be connected to the transmission case main body with the PTO clutch unit and the PTO driven shaft, connected to the PTO clutch unit, engaged with the lid member; thus, the assembling task of the PTO clutch unit is very troublesome.
Further, since the PTO clutch unit and the PTO driven shaft are long in the axial direction, the supporting distance of the assembly consisting of the PTO clutch unit and the PTO driven shaft is long and the stability is not satisfactory.
Moreover, a wasted space is created above the differential gear unit, thereby making the entire length of the transmission case long.
The PTO clutch unit is provided with a brake mechanism depending on the specification of the vehicle.
The brake mechanism is configured to apply/release the braking power to/from the PTO driven shaft when the PTO clutch unit is in the power interrupting state/the power transmitting state, respectively.
More specifically, the brake mechanism comprises a brake member which is relatively non-rotatable with respect to the PTO driven shaft during braking power application, and a fixed part for engaging with the brake member to stop the rotation of the brake member.
However, in the conventional configuration in which the PTO unit is supported by the wall and the lid member, the fixed part cannot be easily arranged, thereby complicating the structure of the transmission case main body.